1. Field of the Invention
The present invention relates to a network device, more particularly, to a network device relating to a digital subscriber line (DSL) such as an asymmetrical DSL (ADSL) or a very high bit rate DSL (VDSL).
2. Description of the Related Art
The growing requirements for internet information have increased the popularity of broadband access services. Digital Subscriber Line (DSL) technology has become a main broadband access technology in the word due to its convenient deployment, good performance, and lower cost.
Asymmetrical Digital Subscriber Line (ADSL) and Very high bit rate Digital Subscriber Line (VDSL) are the most popular kind of DSL technologies. In a typical application, a Customer's Premises Equipment (CPE) is usually configured, controlled, maintained and upgraded by a Central Office (CO). The International Telecommunications Union (ITU) standard G992.1 relating to xDSL prescribes that when an ADSL CPE or a VDSL CPE runs out of power, the ADSL CPE or the VDSL CPE must generate a dying gasp signal, and send the generated dying gasp signal to an ADSL CO or a VDSL CO.
Unfortunately, if the ADSL CPE or the VDSL CPE is completely without power, it cannot operate and send the dying gasp signal to the ADSL CO or the VDSL CO. Accordingly, in the conventional, energy-storage elements, for example capacitors, are taken and equipped into the ADSL CPE or the VDSL CPE, such that when the ADSL CPE or the VDSL CPE runs out of power, the ADSL CPE or the VDSL CPE still can generate the dying gasp signal to the ADSL CO or the VDSL CO in response to the storage of the equipped capacitors.
However, the energies of the equipped capacitors are simultaneously consumed by all of DC-DC converters for generating a plurality of DC operation voltages required by the ADSL CPE or the VDSL CPE when the ADSL CPE or the VDSL CPE runs out of power. In this case, the ADSL CPE or the VDSL CPE may not send the dying gasp signal to the ADSL CO or the VDSL CO. In order to solve such problem, the capacitances of the equipped capacitors are needed to be increased. Nevertheless, the cost of the ADSL CPE or the VDSL CPE is increased by such solution; moreover, the equipped capacitors with high capacitances take up more space on a printed board circuit (PCB) and thus make the layout of the PCB problematic.